<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Title</title>
</head>
<body>

<div id="app">
  <h2 :style="{fontSize:'50px',backgroundColor:'red'}">{{message}}</h2>
  <h2 :style="{fontSize: fs+'px',backgroundColor:fc}">{{message}}</h2>
  <h2 :style="get_style()">{{message}}</h2>
</div>

<script src="../js/vue.js"></script>

<script>
  const app = new Vue({
    el:"#app",
    data: {
      message:"stupid mother fucker",
      fs:'50',
      fc:'red',
    },
    methods:{
      get_style:function (){
        return {fontSize: this.fs + 'px', backgroundColor: this.fc}
      }
    }
  })
</script>
</body>
</html>